Power transmission

ABSTRACT

A pilot operated load compensated variable displacement pump is controlled by a servomotor and a pilot valve to maintain a constant pressure drop across an adjustable orifice in the pump delivery line. The available pressure differential for operating the pilot valve is increased without increasing the pressure drop in the main flow through the adjustable orifice by providing a small restrictor in the operating line to the pilot valve and establishing a continuous bleed flow through that restrictor to establish a large pressure differential supplementing that at the adjustable orifice in the main pump delivery line. The bleed is established through a pressure compensated flow control valve. Maximum pressure limiting is obtained by a pilot relief valve establishing a parallel bleed. Alternatively, a special pilot relief valve establishes both the bleed flow and the maximum pressure limiting.

United States Patent 1191 Lonnemo 1451 Dec. 24, 1974 [73] Assignee: Sperry Rand Corporation, Troy,

Mich.

221 Filed: Dec. 18,1972

21 Appl. N6; 315,945

Primary ExaminerWilliam L. Freeh Assistant Examiner-Gregg Paul LaPointe Attorney, Agent, or Firm-Theodore Van Meter [57] ABSTRACT A pilot operated load compensated variable displacement pump is controlled by a servomotor and a pilot valve to maintain a constant pressure drop across an [52] US Cl. 417/212, 60/450 adjustable orifice in the pump delivery line. The avail- [51] Int. Cl. F04b 1/00 able pressure differential for operating the pilot valve [58] Field of Search 417/213, 218, 220, 221, is increased without increasing the pressure drop in 417/222; 91/506; 60/450 the main flow through the adjustable orifice by providing a small restrictor in the operating line to the pilot [56] References Cited valve and establishing a continuous bleed flow through IT STATES PATENTS that restrictor to establish a large pressure differential 2 255 783 9H9 Kendrick 60,450 supplementing that at the adjustable orifice in the 3 6/1959 Van 60/450 main pump delivery line. The bleed is established 3,067,693 12/1962 Lambeck 1. 417/219 through a Pressure Compensated flow control valve- 3,188,971 6/1965 Puryear 417/222 Maximum pressure limiting is obtained by a pilot relief 3,246,471 4/1966 Goodale 60/450 valve establishing a parallel bleed. Alternatively, a 3,444,689 5/1969 Budzich 60/450 special pilot relief valve establishes both the bleed McMillen CI al. flow and the maximum pressure 3,644,063 2/1972 Bosch 417/213 3,768,928 10/1973 Miller et a1. 417 213 4 Claims, 2 Drawlng Flgul'es LL 5 l8/- L l Z0 POWER TRANSMISSION Conventional load compensated variable displacement pumps have a displacement regulator which is governed by the pressure drop across one or more adjustable orifices in the pump delivery line, thus, automatically regulating the pump delivery to the volumetric flow requirements determined by the size of the adjustable orifice, or orifices. Customarily, such an orifice is found in the variable opening of the usual main directional valve controlling flow to a fluid motor. In such systems, the regulator requires a substantial pressure available for its operation and this is determined by the amount of pressure drop across the adjustable orifice. Thus, if reasonable dynamic behavior is to be had at the regulator, a very substantial pressure drop is imposed upon all of the fluid flowing through the adjustable orifice or directional valve. In systems which transmit large amounts of power hydraulically, this represents a substantial loss through throttling.

The present invention aims to provide an improved load compensated variable displacement pump in which the available pressure for operating the regulator is high, while the pressure drop through the adjustable orifice in the main delivery line is a low one, and thus throttling losses in the main power flow are minimized.

This is achieved by the provision of a pilot operated, load compensated, variable displacement pump for maintaining a predetermined pressure drop across an adjustable orifice which comprises a servomotor for adjusting the pump displacement, a pilot valve for controlling the servomotor, a connection from the pump output ahead of the adjustable orifice for urging the pilot valve toward a position of lesser pump displacement, a connection from the pump output beyond the adjustable orifice for urging the pilot valve toward a position of greater pump displacement, a restrictor in the second connection, and a bleed restriction from the restrictor to maintain a small continuous flow therethrough sufficient to create a pressure drop through the restrictor several times as great as the pressure drop through the adjustable orifice under steady state conditions, whereby a large pressure differential for operating the pilot valve is available without imposing a large pressure drop in the main flow through the adjustable orifice.

In the drawing:

FIG. 1 represents a hydraulic circuit diagram of a pump and control system incorporating a preferred form of the present invention.

FIG. 2 represents a modified form of the present invention.

A variable displacement pump has a servomotor 12 for adjusting its displacement and feeds its output into a delivery line 14. The delivery line 14 leads through an adjustable orifice 16 to a fluid utilization device 18. The adjustable orifice 16 is representative of many types of valves which control the rate of flow to the fluid utilization device, such as one or more fluid motors. In many systems, of which this is typical, the adjustable orifice 16 may comprise a conventional four-way reverse valve.

The servomotor 12 is controlled by a three-way pilot valve 20 which can supply fluid to the servomotor 12 from the supply line through a branch 22 or can exhaust fluid from the servomotor through an exhaust line 24. The pilot valve 20 is urged to the left against a spring 26 by delivery line pressure directed through a brnach 28. Also acting on the pilot valve 20 in opposition to delivery line pressure is a lower pressure derived from the delivery line after passing through the adjustable orifice 16 and a fixed orifice 30. This pressure is transmitted through a branch 32. A continuous bleed flow through the'restrictor 30 is established by a branch 34 containing a pressure compensated flow control valve 36 feeding into the exhaust line 24. For the purpose of establishing a maximum pressure limit in the system, a pilot relief valve 38 is connected as an additional possible bleed from the orifice 30 through a branch 40.

In operation, with the pumplO running and with the servomotor 12 stationary because of the pilot valve 20 being in the neutral position, the pump outlet pressure in lines 14, 22 and 28, transmitted to the right end of pilot valve 20, is exactly balanced by the force of spring 26 and the pressure maintained in line 32 on the left end of pilot valve 20. This pressure is determined by the sum of the pressure drops through the adjustable orifice l6 and the restrictor 30. The pressure drop at restrictor 30 is determined by the setting of the flow control valve 36 which determines the fixed and continuous bleed flow through the restrictor 30.

When the adjustable orifice 16 is changed to a more restricted position, for example, this causes a temporary pressure rise in conduits 14, 22 and 28 which shifts the pilot valve 20 to the left admitting pressure fluid to the servomotor l2 and reducing the pump displacement. Motion of the valve 20 to the left pumps a small quantity of fluid upwardly through line 32 into the bleed circuit thus reducing the flow rate through restrictor 30 and consequently reducing the pressure at its outlet. When the pump displacement has been reduced to the value necessary to maintain the previous pressure drop through the adjustable orifice 16, the valve 20 will return to its neutral position. A similar but opposite action occurs upon an opening adjustment of orifice 16. Whenever the system pressure rises above a predetermined limit, the pilot relief valve 38 will open, causing a further bleed flow through the orifice 30, thus dropping the pressure in conduit 32 and allowing pilot valve 20 to shift to the left and reduce the pump displacement until the pressure overload has ceased.

The pressure available for operating pilot valve 20 is theoretically the sum of the pressure drops through adjustable orifice 16 and restrictor 30. By making the latter pressure drop relatively high, say five times as high as the former pressure drop, it will be seen that effective control of the pilot valve 20 is maintained without imposing a large pressure drop through the adjustable orifice 16. In this way, substantial power losses in the main flow line are avoided.

In the modification illustrated in FIG. 2, a special pilot relief valve 42 is provided to take the place of the flow control valve 36 and the pilot relief valve 38 together. Thus the inner spring 44 of the relief valve poppet is adjusted automatically by means of a piston 46 having a diameter equal to the seat diameter of the poppet. A head 48 limits the stroke of piston 46 and a branch line 50 connects the piston 46 to a point ahead of the restrictor 30. An auxiliary spring 52 aids in biasing the piston 46 against this pressure.

Thus, depending upon the pressure drop across the restrictor 30, the piston 46 will take up a certain position balancing this pressure drop against the force of springs 44 and 52 and will vary the pressure setting of the pilot relief valve 42 correspondingly. A continuous quiescent flow is accordingly maintained through restrictor 30 which is at a substantially constant rate because of the constant pressure drop across restrictor 30.

I claim:

1. A pilot operated load compensated variable displacement pump for maintaining a predetermined pressure drop across an adjustable orifice comprising a servomotor for adjusting the pump displacement, a pilot valve for controlling the servomotor, a connection from the pump output ahead of the adjustable orifice for urging the pilot valve toward a position of lesser pump displacement, a second connection from the pump output beyond the adjustable orifice for urging the pilot valve toward a position of greater displacement, a restrictor in the second connection and a bleed restriction comprising a pressure responsive flow regulator from the restrictor to maintain a small and fixed continuous flow therethrough independent of system pressure and sufficient to create a pressure drop through the restrictor several times as great as the pressure drop through the adjustable orifice under steady state conditions, whereby a large pressure differential for operating the pilot valve is available without imposing a large pressure drop in the main flow through the adjustable orifice.

2. A pump as defined in claim 1 wherein the flow regulator comprises an additional restrictor and a compensator for maintaining a constant pressure drop across the additional restrictor.

3. A pump as defined in claim 1 which includes a pilot relief valve connected to the restrictor to limit the maximum pump output pressure.

4. A pump as defined in claim 2 having a pilot relief valve connected to the first restrictor to limit the maxi mum pump output pressure. 

1. A pilot operated load compensated variable displacement pump for maintaining a predetermined pressure drop across an adjustable orifice comprising a servomotor for adjusting the pump displacement, a pilot valve for controlling the servomotor, a connection from the pump output ahead of the adjustable orifice for urging the pilot valve toward a position of lesser pump displacement, a second connection from the pump output beyond the adjustable orifice for urging the pilot valve toward a position of greater displacement, a restrictor in the second connection and a bleed restriction comprising a pressure responsive flow regulator from the restrictor to maintain a small and fixed continuous flow therethrough independent of system pressure and sufficient to create a pressure drop through the restrictor several times as great as the pressure drop through the adjustable orifice under steady state conditions, whereby a large pressure differential for operating the pilot valve is available without imposing a large pressure drop in the main flow through the adjustable orifice.
 2. A pump as defined in claim 1 wherein the flow regulator comprises an additional restrictor and a compensator for maintaining a constant pressure drop across the additional restrictor.
 3. A pump as defined in claim 1 which includes a pilot relief valve connected to the restrictor to limit the maximum pump output pressure.
 4. A pump as defined in claim 2 having a pilot relief valve connected to the first restrictor to limit the maximum pump output pressure. 